[PATCH v3 2/2] iio: health: max30100: Make LED pulse-width configurable via DT

[Shrikant Raskar <raskar.shree97@gmail.com>]

The required LED pulse width depends on board-specific optical and
mechanical design, which affects measurement accuracy and power use.
Making it configurable via Device Tree allows each platform to define
an appropriate value instead of relying on a hardcoded default.

If unspecified, the driver defaults to 1600 us for backward compatibility.

Tested on: Raspberry Pi 3B + MAX30100 breakout board.

Reviewed-by: Nuno Sa <nuno.sa@analog.com>
Signed-off-by: Shrikant Raskar <raskar.shree97@gmail.com>
---
Changelog:
Changes since v2:
- Reorder SPO2_CONFIG register defines by bit position (lowest to highest).
- Add missing header file for FIELD_PREP() macro.
- Add Reviewed-by tag.

Link to v2:
https://lore.kernel.org/all/20251008031737.7321-3-raskar.shree97@gmail.com/
---
 drivers/iio/health/max30100.c | 38 ++++++++++++++++++++++++++++++++---
 1 file changed, 35 insertions(+), 3 deletions(-)

diff --git a/drivers/iio/health/max30100.c b/drivers/iio/health/max30100.c
index 814f521e47ae..3d441013893c 100644
--- a/drivers/iio/health/max30100.c
+++ b/drivers/iio/health/max30100.c
@@ -5,7 +5,6 @@
  * Copyright (C) 2015, 2018
  * Author: Matt Ranostay <matt.ranostay@konsulko.com>
  *
- * TODO: enable pulse length controls via device tree properties
  */
 
 #include <linux/module.h>
@@ -18,6 +17,7 @@
 #include <linux/mutex.h>
 #include <linux/property.h>
 #include <linux/regmap.h>
+#include <linux/bitfield.h>
 #include <linux/iio/iio.h>
 #include <linux/iio/buffer.h>
 #include <linux/iio/kfifo_buf.h>
@@ -52,9 +52,13 @@
 #define MAX30100_REG_MODE_CONFIG_PWR		BIT(7)
 
 #define MAX30100_REG_SPO2_CONFIG		0x07
+#define MAX30100_REG_SPO2_CONFIG_PW_MASK	GENMASK(1, 0)
+#define MAX30100_REG_SPO2_CONFIG_200US		0x0
+#define MAX30100_REG_SPO2_CONFIG_400US		0x1
+#define MAX30100_REG_SPO2_CONFIG_800US		0x2
+#define MAX30100_REG_SPO2_CONFIG_1600US		0x3
 #define MAX30100_REG_SPO2_CONFIG_100HZ		BIT(2)
 #define MAX30100_REG_SPO2_CONFIG_HI_RES_EN	BIT(6)
-#define MAX30100_REG_SPO2_CONFIG_1600US		0x3
 
 #define MAX30100_REG_LED_CONFIG			0x09
 #define MAX30100_REG_LED_CONFIG_LED_MASK	0x0f
@@ -306,19 +310,47 @@ static int max30100_led_init(struct max30100_data *data)
 		MAX30100_REG_LED_CONFIG_LED_MASK, reg);
 }
 
+static int max30100_get_pulse_width(unsigned int pwidth_us)
+{
+	switch (pwidth_us) {
+	case 200:
+		return MAX30100_REG_SPO2_CONFIG_200US;
+	case 400:
+		return MAX30100_REG_SPO2_CONFIG_400US;
+	case 800:
+		return MAX30100_REG_SPO2_CONFIG_800US;
+	case 1600:
+		return MAX30100_REG_SPO2_CONFIG_1600US;
+	default:
+		return -EINVAL;
+	}
+}
+
 static int max30100_chip_init(struct max30100_data *data)
 {
 	int ret;
+	int pulse_width;
+	/* set default LED pulse-width to 1600 us */
+	unsigned int pulse_us = 1600;
+	struct device *dev = &data->client->dev;
 
 	/* setup LED current settings */
 	ret = max30100_led_init(data);
 	if (ret)
 		return ret;
 
+	/* Read LED pulse-width-us from DT */
+	device_property_read_u32(dev, "maxim,pulse-width-us", &pulse_us);
+
+	pulse_width = max30100_get_pulse_width(pulse_us);
+	if (pulse_width < 0)
+		return dev_err_probe(dev, pulse_width, "invalid LED pulse-width %uus\n", pulse_us);
+
 	/* enable hi-res SPO2 readings at 100Hz */
 	ret = regmap_write(data->regmap, MAX30100_REG_SPO2_CONFIG,
 				 MAX30100_REG_SPO2_CONFIG_HI_RES_EN |
-				 MAX30100_REG_SPO2_CONFIG_100HZ);
+				 MAX30100_REG_SPO2_CONFIG_100HZ |
+				 FIELD_PREP(MAX30100_REG_SPO2_CONFIG_PW_MASK, pulse_width));
 	if (ret)
 		return ret;
 
-- 
2.43.0